There is much current interest in lipid hydroperoxides in terms of evaluating their importance as a primary mechanism of tissue injury. Lipid hydroperoxides have been implicated in atherosclerosis, stroke, diabetes, emphysema due to exposure to pollution, cancer, drug toxicity, and aging. Ethanol, several xenobiotics and anthracycline antibiotics (which are currently employed in cancer chemotherapy) stimulate the generation of lipid hydroperoxides by tissues, and these peroxides may be related to the tissue damage caused by the formentioned stimulators. Research groups in Japan are now screening blood samples for hydroperoxides as an indicator of the extent of burn injury [I. Nishigaki et al. (1980) Biochem. Med. 24, 185-189] and in patients with diabetes [Y. Sato et al. (1979) Biochem. Med. 21, 104-107; I. Nishigaki et al. (1981) Biochem. Med. 25, 373-378.]. Lipid peroxidation has important pathophysiologic consequences for cells since some of the oxidized products can serve as highly potent biological agents [H. D. Perez, B. B. Heksler, and I. M. Goldstein (1980) Inflammation 4, 313] and others can be deleterious to cell membranes [J. W. Bridges, D. J. Benford, and S. A. Hubbard (1983) Ann. N.Y. Acad. Sci. 407, 42]. Small amounts of lipid hydroperoxides are known to acitvate prostaglandin H synthase (International Union of Biochemistry index EC1.14.99.1) in vitro [M. E. Hemler and W. E. M. Lands (1980) J. Biol. Chem. 255, 6253], although their precise role has been difficult to evaluate due to the lack of a sufficiently specific and sensitive analytical method.
Despite the emerging importance of lipid hydroperoxides, all of the currently available methods for the assay of lipid hydroperoxides in biological samples have serious limitations. The most widely used method, the thiobarbiturate assay [A. Ottolenghi (1959) Arch. Biochem. Biophys. 79, 355-363] actually measures a malondialdehyde-like substance, which results during the decomposition of the endoperoxides [B. Barber (1967) Adv. in Gerontol. Res. 2, 355-397]. Malondialdehyde may arise from sources other than lipid hydroperoxides, and whereas 0.1-0.5 .mu.M malondialdehyde may be detected, the efficiency of conversion of lipid hydroperoxides to malondialdehyde is only about 5% [T. Asakawa and S. Matsushita (1980) Lipids 15, 137-140]. Thus, the measurement of malondialdehyde is neither specific nor sensitive. A gas chromatography-based assay depends upon the decomposition of lipid hydroperoxides to form ethane and pentane [C. J. Dillard and A. L. Tappel (1979) Lipids 14, 989-995]or ethylene [M. Lieberman and P. Hochstein (1966) Science 152.213-214]. These gases can be measured accurately at low concentration, but this assay is limited to the estimation of the extent of lipid peroxidation occurring during an incubation period, and is not useful for the determination of the concentration of lipid hydroperoxides in, for example, blood plasma. Other assays utilize the chemiluminescence and fluorescence which accompany the process of lipid peroxidation. Not only is the basis for the light emission unclear [R. M. Howes and R. H. Steele (1971) Resh. Commun. Chem. Path. Pharmacol. 2,619-625], but these assays are only able to measure peroxides formed during the incubation period, and thus suffer from the same limitations as the measurement of volatile hydrocarbons in that they are not applicable to the determination of the level of lipid peroxide already in a sample.